Daily Network Monitor

Saw this great blog posting on ZDNet recently…

E-Way Technology Systems is a company from Taiwan that is selling a tiny 200 MHz x86-compatible fanless mini PC with 128 MB RAM, Fast Ethernet, and front loading compact flash slot for $99 at single quantities! Of course this wouldn’t be very useful as a full desktop computer, but it is the perfect low-power fanless zero-moving-part silent appliance at an unbelievably low price. Here are some of the things you can do with this hundred dollar box.

Citrix or Terminal Server thin client (you’ll need to add keyboard, mouse, and a display). By the time you add those things, you might be up to $300 but it’s multiples cheaper than other thin clients.
Small office or home office Asterisk PBX to support a couple of phones and voice mail boxes (So long as you don’t try to transcode anything).
Change to a board with no video and audio but with multiple Ethernet ports and this can become a killer IPCop appliance.
The front loading CF (Compact Flash) slot is super convenient for firmware upgrades since you can easily extract the CF card and flash the image from a regular computer.
It could probably serve as a Linux Wi-Fi appliance as well with an
But this hundred dollar unit is a little under powered and I couldn’t help but wonder if there is a more powerful solution. I went to E-Way’s website and found this 800 MHz fanless mini-ITX system with 256 MB RAM for a mere $199 at single quantities ($150 at 300 units). But even at $199, you can’t even build a mini-ITX system this cheap in component costs alone! Mini-ITX components are usually very expensive.

It doesn’t have the front loading CF slot but it has a PXE boot ROM and very good performance characteristics. This unit can use CF or hard drives in the thicker model. This would probably make the perfect PBX system if it was coupled with something like the Astrabank-8 which is a USB device that provides 8 analog phone ports for analog phones or fax machines. The performance and hard drive would allow it to handle many more users and voice mail boxes.

It could probably handle DVD playback with ease since it has MPEG 2 acceleration though I doubt if it will handle HD video play back. As a media PC, it has limitations because it lacks HD component out and only has a DB-15 VGA port and no DVI. But it would probably make a killer car PC since it doesn’t use a lot of power (no more than 20 watts) and you could hook up an LCD panel to it. It’s small enough to easily mount under the car seat. As a firewall appliance, it would need to have more Ethernet ports though I’m not sure if that’s an option with this mini chassis or not. E-Way does sell 3 and 4 port fanless systems that are perfect for the firewall appliance which may even be fast enough to do in-line virus scanning for a small number of users.

This story appeared in Network World here.

“We are used to breaking products in lab testing, but this time we broke 802.11 itself. Our tests uncovered a design flaw in the Wi-Fi protocol that affects performance testing, not just for current 802.11a/g products, but possibly in upcoming 802.11n gear as well. As a result of our tests, an IEEE committee heard a proposal to recognize and fix the design flaw.

It’s a common misperception that Wi-Fi is an inherently “lossy” medium. Wi-Fi is highly vulnerable to signal errors, but it compensates with built-in error checking and retransmission mechanisms. Even a huge error rate (say, 10% of all packets, the maximum allowed in 802.11) should still result in zero loss, because packet errors are retransmitted.
That’s the theory. In practice, we found a deficiency in an 802.11 packet header that can lead to packet loss.

The physical layer convergence procedure (PLCP) header carries key information about each packet, such as its length and transmission rate. While the rest of an 802.11 packet has excellent error protection because of a 32-bit CRC field, the PLCP header has only a single bit for error checking, and that is nowhere near enough to protect against corruption.

Weak PLCP error checking can fool an 802.11 receiver into believing that it never received packets, even after a transmitter goes through multiple retry attempts.

For example, suppose an 802.11g transmitter sends a 100-byte packet at 54Mbps, and that channel noise corrupts the PLCP header. The corrupted header can convey bogus values, such as telling the receiver the packet is 4,095 bytes long and is being sent at 6Mbps.

An uncorrupted packet would take just 36 microsec to transmit, but in this case the corrupted PLCP header will cause the receiver to keep listening for the packet for 5,484 microsec. The receiver is literally off the air for that long period, causing it to miss multiple retry attempts and give up on the packet as lost.

This perceived loss makes it harder to get an accurate read on device performance. It’s standard practice in throughput and latency tests to tolerate zero dropped packets. Because weak error checking in the PLCP header introduces packet loss, lower throughput rates are a likely result.

Weak error handling also can affect roaming tests. If a receiver misses an Extensible Authentication Protocol handshake packet during a roaming event, it can take 30 seconds before the RADIUS handshake begins again. We saw some 30-second roaming times in our tests because of this issue.

The probability of PLCP corruption with short packets and high rates is around one in 1,000. Because performance tests inevitably involve far more than 1,000 packets, results easily can be skewed downward by corrupted PLCP headers.

We compensated for this issue by setting an acceptable loss threshold of 0.1% in our throughput tests. We’re not crazy about allowing loss in throughput tests. It’s a violation of RFCs 1242 and 2544, and it’s a common dodge used by vendors of poorly performing products.

In the absence of a better solution, however, we opted for the acceptable packet loss to mask any instances of PLCP header corruption.

While there’s no chance of changing the 802.11a/g standard because of backward compatibility issues, it’s not too late for the IEEE to correct this design flaw in the forthcoming 802.11n standard. The IEEE recently heard a proposal to address the issue uncovered in these tests.

At the IEEE 802.11 meeting in Melbourne in September, test equipment maker VeriWave and Wi-Fi switch vendor Aruba Wireless Networks jointly outlined the problem and described its implications for performance testing. The current 802.11n draft uses the same PLCP structure as 802.11a/g when operating in mixed mode (with 802.11b/g clients present). The presenters recommended stronger error protection for 802.11n mixed-mode operation, as well as warning language in the forthcoming 802.11.2 standards to alert testers to the design flaw.

An obvious question is why this phenomenon hasn’t been seen before. The answer has much to do with the relatively crude state of Wi-Fi performance testing. Besides the perception that “it’s just wireless,” previous tests haven’t offered enough packets at high enough rates, and closely analyzed the results, to understand that the current 802.11 protocol is itself an impediment to improved performance.”

Cisco Systems has agreed to buy Greenfield Networks in a move designed to expand its Ethernet lineup, the companies said earlier this week.
Greenfield, a privately held Sunnyvale, Calif.-based company with 60 employees, develops semiconductors designed to improve Ethernet packet processing for the so-called metro Ethernet market. Telecommunications carriers use the technology to string together a number of corporate networks within a metropolitan-area network, allowing these companies to use VoIP and data over their networks.

“By integrating Greenfield Networks technology with Cisco’s family of metro Ethernet switches, we will be able to improve the time to market of new carrier-class features to our service provider partners,” Kathy Hill, senior vice president of Cisco’s Ethernet and Wireless Technology Group, said in a statement.

Greenfield, which also has offices in Bangalore, India, was founded in 2000. Cisco plans to fold Greenfield’s product portfolio and employees into Hill’s group, once the deal closes during Cisco’s current fiscal quarter, which ends in late January. Financial terms of the deal were not disclosed.

The networking giant has been building up its metro Ethernet offerings over a number of years, as the concept of metro Ethernet has become mainstream.